Apparatus and methods for injecting filler material into a hole in a composite layer

ABSTRACT

Apparatus and methods for injecting molten filler material into a hole. The method in accordance with one embodiment comprises: drilling a hole in a composite layer; heating filler material comprising an electrically conductive low-melting alloy to a molten state; inserting a nozzle having an internal channel system into the hole with a gap separating the nozzle and the hole; forcing molten filler material into, through and out of the internal channel system of the nozzle and into the gap; and retracting the nozzle from the hole. The nozzle may be rotary or not rotary.

BACKGROUND

This disclosure generally relates to the use of fasteners to secure twoor more structures or workpieces (at least one of which is made ofcomposite material, such as fiber-reinforced plastic) in a manner suchthat high interference fit of the fasteners within their respectiveholes in the structures is achieved. In particular, this disclosurerelates to apparatus and methods for fastening a layer of compositematerial to another layer of material using an interference fit fastenerassembly having a bolt or a pin and a mating part (e.g., a nut or acollar).

As used herein, the category “mating parts” comprises internallythreaded nuts and collars and swaged collars. As used herein, thecategory “fasteners” includes bolts and pins. As used herein, the term“external projections” should be construed broadly to encompass at leastthe following types: (1) external threads and (2) external annularrings. As used herein, the term “hole” means a surface that bounds aspace having openings at opposing ends. In the context offiber-reinforced plastic material, the surface bounding the space may beformed by resin and fibers.

At least one method for fastening multiple layers of material togetheris to clamp up the layers, drill holes, and then insert some type offastener into the holes and thereby secure the layers together. Thefasteners are usually inserted in a net or clearance fit in thereceiving holes in the layers. For many applications, this will besufficient. However, when the assembled structure is subjected to cyclicloading, the looseness of the fit of the fasteners within their holescan result in continual working of the fasteners within their holes.

Additional challenges are presented when one or more of the fastenedlayers are made of composite material. For example, carbonfiber-reinforced plastics (CFRP) are considerably less conductive thanmetal. Electrical current is conducted through carbon fibers in the CFRPstructure. Any discontinuity between the carbon fibers and the metallicsleeve or pin in the CFRP hole is undesirable. One way to avoiddiscontinuity in CFRP joints is to incorporate sleeved fastenersinstalled in an interference fit condition to achieve closer proximityof the carbon fiber to the fastener.

An interference fit of the fastener (hereinafter “interference fitfastener”) in the hole can effectively reduce discontinuities due tocyclic loading of the assembled structure. Interference creates atighter joint that reduces movement, resulting in enhanced fatigueperformance. Additionally, interference fit fasteners can help ensuresafe dissipation of electrical current.

SUMMARY

The subject matter disclosed in some detail below is directed toapparatus and methods for minimizing the variation in interference fitfor sleeveless fasteners used to fasten a layer of composite material(hereinafter “composite layer”) to another layer of material (e.g., ametallic layer or another composite layer), while enhancing theelectrical conductivity between the fibers of the composite material andthe metallic interference fit fastener. The apparatus comprises a nozzleconfigured to coat a hole with molten filler material. When the moltenfiller material solidifies, the resulting coated hole will have adiameter defined by the external diameter of the nozzle. This methodwill greatly reduce the variability of hole diameters and allow for lessvariation in the interference levels between the fastener and thestructure (reducing process variation and allowing for increased cutterlife). By pressing the electrically conductive filler material into thecrevices or voids in the hole surface, the electrical conductivity willbe improved as well as the fatigue life and fluid-tight properties.

Although various embodiments of apparatus and methods for minimizinginterference fit variation and enhancing electrical conductivity in aninterference fit fastener assembly will be described in some detailbelow, one or more of those embodiments may be characterized by one ormore of the following aspects.

One aspect of the subject matter disclosed in detail below is a methodfor injecting molten filler material into a hole, the method comprising:(a) drilling a hole in a composite layer; (b) heating filler materialcomprising an electrically conductive low-melting alloy to a moltenstate; (c) inserting a nozzle having an internal channel system into thehole with a gap separating the nozzle and the hole; (d) forcing moltenfiller material into, through and out of the internal channel system ofthe nozzle and into the gap; and (e) retracting the nozzle from thehole. The nozzle is retracted until the nozzle is completely removedfrom the hole, following which a fastener is inserted into the hole withan interference fit. The method may further comprise heating thefastener before insertion.

In accordance with some embodiments, the method described in thepreceding paragraph further comprises rotating the nozzle as moltenfiller material exits the nozzle. In example embodiments, the moltenfiller material exits the nozzle through a plurality ofcircumferentially distributed side openings.

In accordance with other embodiments, the molten filler material exitsthe nozzle during retraction of the nozzle. In one proposedimplementations, the molten filler material exits the nozzle through acircumferential opening and is redirected and pushed in a directionhaving a radially outward component by a contoured flow-redirectingsurface of the nozzle during retraction of the nozzle.

Another aspect of the subject matter disclosed in detail below is anapparatus for injecting molten filler material into a hole, theapparatus comprising: a reservoir for storing molten filler materialthat is electrically conductive; a pump assembly in fluid communicationwith the reservoir; and a nozzle in fluid communication with the pumpfor receiving the molten filler material pumped from the reservoir andejecting the molten filler material. The nozzle comprises: a proximalbody portion having an internal volume in fluid communication with thepump; an intermediate body portion comprising a plurality oflongitudinal melt channels configured to guide molten filler materialentering from the internal volume of the proximal body portion to flowparallel to a longitudinal axis of the nozzle and away from the proximalbody portion; and a distal body portion comprising a flow-redirectingsurface configured to divert longitudinally flowing molten fillermaterial exiting the intermediate body portion to flow radially outward.A portion of the flow-redirecting surface of the distal body portion anda portion of the intermediate body portion define a circularcircumferential orifice. In accordance with one embodiment, theapparatus further comprises: a retraction mechanism for retracting thenozzle; a control computer configured with programming for controlling arate of rotation of the pump and a rate of displacement of theretraction mechanism during a filling operation; and a heating elementdisposed inside the nozzle.

In accordance with one embodiment of the apparatus described in thepreceding paragraph: the intermediate body portion of the nozzlecomprises an outer circumferential wall having a circular terminalportion; the portion of the intermediate body portion that partlydefines the circular circumferential orifice comprises the circularterminal edge of the outer circumferential wall; and theflow-redirecting surface of the distal body portion of the nozzle is acircumferential surface of revolution having a diameter that increasescontinuously to a maximum diameter of the distal body portion that isgreater than an outer diameter of the outer circumferential wall.

A further aspect of the subject matter disclosed in detail below is anapparatus for injecting molten filler material into a hole, theapparatus comprising: a reservoir for storing molten filler materialthat is electrically conductive; a pump assembly in fluid communicationwith the reservoir; a rotary nozzle in fluid communication with the pumpfor receiving the molten filler material pumped from the reservoir andejecting the molten filler material; and a motor 60 for driving rotationof the rotary nozzle. The rotary nozzle comprises a circular cylindricalintermediate body portion having an internal channel system and aplurality of circumferentially distributed side openings that extend alength of the circular cylindrical intermediate body portion and allowmolten filler material to flow radially outward from the nozzle. Theplurality of side openings are either all linear or all helical. Inaccordance with one embodiment of the rotary nozzle, respective pairs ofbeveled projections are disposed at opposite edges of each side opening.

Yet another aspect is a structural assembly 5 for an aircraft, theassembly comprising: a composite layer having a hole with a relativelyrough surface that has concavities; and a coating adhered to therelatively rough surface of the hole and filling the concavities, thecoating defining a smooth circular cylindrical surface of a coated hole,wherein the composite layer comprises fibers made of electricallyconductive material, and the coating comprises an electricallyconductive low-melting alloy.

Other aspects of apparatus and methods for injecting molten fillermaterial into a hole in a composite layer are disclosed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, functions and advantages discussed in the precedingsection can be achieved independently in various embodiments or may becombined in yet other embodiments. Various embodiments will behereinafter described with reference to drawings for the purpose ofillustrating the above-described and other aspects.

FIGS. 1A through 1D are diagrams representing respective sectional viewsof a layer of composite material during four stages of a method forcoating a previously drilled hole in the composite material and theninserting a fastener into the coated hole in accordance with oneembodiment.

FIGS. 2A and 2B are diagrams representing respective longitudinallysectioned isometric views of one example of a nozzle for injectingelectrically conductive molten filler material into a gap between thenozzle and surface(s) of a hole in the composite material in accordancewith the method partly depicted in FIGS. 1A-1D.

FIG. 2C is a diagram showing a portion of the nozzle depicted in FIG. 2Aon a magnified scale, which portion is indicated by the ellipse 2C inFIG. 2A.

FIG. 3 is a hybrid diagram showing physical and operationalrelationships of some components of an apparatus for coating a surfaceof a countersunk hole in composite material with electrically conductivematerial using a linearly retracting and non-rotary nozzle of the typedepicted in FIGS. 2A and 2B.

FIG. 4 is a diagram representing one view of a nozzle having a pluralityof circumferentially distributed longitudinal linear openings inaccordance with one embodiment.

FIG. 4A is a diagram showing a portion of the nozzle depicted in FIG. 4on a magnified scale, which portion is indicated by the circle 4A inFIG. 4.

FIG. 5 is a diagram representing another view of the nozzle depicted inFIG. 4.

FIG. 5A is a diagram showing a portion of the nozzle depicted in FIG. 5on a magnified scale, which portion is indicated by the circle 5A inFIG. 5.

FIG. 5B is a diagram showing a portion of the nozzle depicted in FIG. 5on a magnified scale, which portion is indicated by the circle 5B inFIG. 5.

FIGS. 6A and 6B are diagram representing respective views of a rotarynozzle having a plurality of circumferentially distributed helicalopenings in accordance with another embodiment.

FIG. 7 is a hybrid diagram showing physical and operationalrelationships of some components of an apparatus for coating a surfaceof a countersunk hole in composite material with electrically conductivematerial using a rotary nozzle.

FIG. 8 is a hybrid diagram showing physical and operationalrelationships of some components of an apparatus for coating a surfaceof a flush hole in composite material with electrically conductivematerial using a rotary nozzle.

FIG. 9 is a block diagram identifying some additional components of theapparatus partly depicted in FIG. 3.

FIG. 10 is Table 1 listing sample compositions of filler materialscomprising gallium-based alloys of liquid metal combined with a puresolid metal or with a solid metal alloy.

FIG. 11 is a diagram representing a partially sectioned view of anassembly comprising composite and metallic structures gripped by asleeveless interference fit fastener assembly.

FIG. 12 is a flowchart identifying steps of a method for injectingmolten filler material into a hole in accordance with one embodiment.

Reference will hereinafter be made to the drawings in which similarelements in different drawings bear the same reference numerals.

DETAILED DESCRIPTION

Various embodiments of apparatus and methods for injecting molten fillermaterial into a hole in a composite layer will now be described indetail for the purpose of illustration. The apparatus and methods can beused to minimize interference fit variation and enhance electricalconductivity in an interference fit fastener assembly. At least some ofthe details disclosed below relate to optional features or aspects,which in some applications may be omitted without departing from thescope of the claims appended hereto.

In particular, one illustrative embodiment of a structural assemblycomprising a first structural element made of metallic material (e.g., ametal alloy) attached to a second structural element made of compositematerial (e.g., fiber-reinforced plastic) by means of an interferencefit fastener assembly is described in detail below. However, inalternative examples, the first and second structural elements can bothbe made of composite material. In addition, it should be appreciatedthat the concepts disclosed herein also have application in theattachment of three or more structural elements together.

In accordance with the aforementioned illustrative embodiment, thefastener comprises a pin and the mating part comprises a swaged collarthat is interengaged with the external projections of the mating portionof the pin. However, the concepts disclosed herein also have applicationin other embodiments in which the fastener comprises a bolt and themating part comprises a nut having internal threads that areinterengaged with the external projections of the mating portion of thebolt.

The method proposed herein for fastening two or more layers ofstructural material together (at least one layer being made of compositematerial, e.g., carbon fiber-reinforced plastic) comprises the followingsteps performed independently for each composite layer: (a) drilling ahole in a composite layer; (b) heating filler material comprising anelectrically conductive low-melting alloy to a molten state; (c)inserting a nozzle having an internal channel system into the hole witha gap separating the nozzle and the hole; (d) forcing molten fillermaterial into, through and out of the internal channel system of thenozzle and into the gap; and (e) retracting the nozzle from the hole.

After all holes in all layers of composite material have been coatedwith filler material, those layers of composite material and any otherlayers made of a structural material other than composite material areplaced in a stack such that the holes in the respective stacked layersare aligned. A respective fastener is pre-heated (to liquefy the surfaceof the solidified material to enable hydroplaning during insertion,thereby reducing resistance) and then inserted into a respective stackof aligned holes so that a shank of the fastener passes through thecoated hole in the layer of composite material with an interference fitand a mating portion of the fastener extends beyond the outermost layerof structural material on the other side of the stack. A respectivemating part that abuts that outermost layer is then coupled to themating portion of the respective fastener. In each instance, the resultis an interference fit fastener assembly in which at least a portion ofthe shank of the fastener is surrounded by electrically conductivematerial on the surface of the coated hole in the composite material.

The method described in the preceding paragraph may be used to coatholes in composite material that have a counterbore or a countersink inan uppermost portion of the hole. The method further comprises guidingflowing molten filler material to coat a surface of the counterbore orcountersink. In accordance with alternative embodiments, the method canbe used to coat holes in composite material that have neither acounterbore nor a countersink.

FIGS. 1A through 1D are diagrams representing respective sectional viewsof a composite layer 30 made of composite material having a countersunkhole 20 during four stages of one embodiment of the method describedabove. This embodiment involves concurrent incremental filling of thegap 15 along a depth of the gap during retraction of the nozzle 12.

FIGS. 1A and 1B show two instances in time subsequent to insertion of anozzle 12 into a hole 20, which has been previously drilled in acomposite layer 30 and subsequent to start of the filling process.During the filling process, a molten filler material 11 comprising anelectrically conductive low-melting alloy is forced into and through aninternal channel system 13 formed inside the body of the nozzle 12 andthen out of a circular circumferential orifice 18 of the nozzle 12,exiting (i.e., being injected) into a gap 15 separating nozzle 12 andhole 20 during nozzle retraction. The direction of linear displacementof the nozzle 12 during molten filler material injection and nozzleretraction is indicated by the arrow located above the nozzle 12 inFIGS. 1A and 1B.

In accordance with the embodiment depicted in FIGS. 1A and 1B, thenozzle 12 includes a circular circumferential orifice 18 and a distalbody portion 16 disposed below the circular circumferential orifice 18.The distal body portion 16 in this example has a contouredflow-redirecting surface (not numbered in FIGS. 1A and 1B, but seeflow-redirecting surface 80 b in FIG. 2C) that partly defines thecircular circumferential orifice 18 and a circular cylindrical outercircumferential surface 84 having an outer diameter D. FIG. 1A shows thedistal body portion 16 at a first elevation inside the hole 20 at aparticular time, while FIG. 1B shows the distal body portion 16 at asecond elevation at a later time, i.e., after the nozzle 12 has furtherretracted by the difference in respective depicted elevations. Thedistal body portion 16 displaces linearly upward in the hole 20 asmolten filler material 11 exits the circular circumferential orifice 18.As the distal body portion 16 displaces upward, the flow-redirectingsurface 80 b redirects and pushes the molten filler material 11 towardthe surface of the hole 20, causing the molten filler material 11 tofill any concavities in the hole surface. Concurrently, the circularcylindrical outer circumferential surface 84 shapes the molten fillermaterial 11 in the gap 15 to form a coating 11 a having an averagethickness δ with a smooth circular cylindrical surface 31 having aninternal diameter D, which is the same as the outer diameter of thecircular cylindrical outer circumferential surface 84.

In the example depicted in FIGS. 1A and 1B, the hole 20 has acountersink (i.e., a chamfer 21) at the top of the hole 20. The chamfer21 is also coated with the molten filler material 11 during the fillingprocess. Coating the chamfer 21 is accomplished using a flexible end cap22 having a conical portion 24 separated from the surface of the chamfer21 by a conical gap 23, which conical gap 23 will be ultimately filledwith molten filler material 11, as depicted in FIG. 1B. As seen in FIG.1B, a volume of space under the end cap 22 and above the conical portion24 is also filled with excess molten filler material 11. The excessfiller material 11 is removed by a recycling pump 56 via a pipe 26 andreturned to a molten filler material reservoir (not shown in FIGS. 1Aand 1B, but see reservoir 54 shown in FIG. 3) via a pipe 28. When thedistal body portion 16 reaches the conical portion 24 of the flexibleend cap 22, retraction of the nozzle 12 is stopped, the remaining excessfiller material 11 is removed, and the molten filler material 11 coatinghole 20 is allowed to cool to form the coating 11 a.

During the cooling (i.e., curing) process, the filler material 11solidifies to form a coating 11 a. The end result (partly depicted inFIG. 1C) is a coated hole 20 a. As previously mentioned, the compositelayer 30 is then placed in a stack with other layers of structuralmaterial (e.g., other layers of composite material that have undergonethe same hole coating process) and a fastener 7 (shown in FIG. 1D) isinstalled in the hole. The fastener 7 can be heated prior to insertionto reduce friction during insertion. In the example depicted in FIG. 2D,fastener 7 has a head 4 and a shank 6. A threaded portion 8 of fastener7 is shown in FIG. 11. As seen in FIGS. 1D and 11, the head 4 and shank6 of the fastener 7 are in contact with the coating 11 a.

FIGS. 2A and 2B are diagrams representing respective longitudinallysectioned isometric views of one example of a nozzle 12 for injectingelectrically conductive molten filler material 11 into a gap 15 definedbetween the nozzle 12 and a hole 20 in a composite layer 30. FIG. 2C isa diagram showing a portion of the nozzle depicted in FIG. 2A on amagnified scale, which portion is indicated by the ellipse 2C in FIG.2A.

The nozzle 12 depicted in FIGS. 2A-2C includes a proximal body portion70, an intermediate body portion 72, and a distal body portion 16. Theproximal body portion 70 is cup-shaped and has an internal volume 71.The intermediate body portion 72 has a channel system 13. The channelsystem 13 includes a plurality of longitudinal melt channels 86, anannular longitudinal melt channel 14 a, and a release melt channel 14 bwhich may have a conical or continuously curved shape. The plurality oflongitudinal melt channels 86 open at one end into the internal volume71 of the proximal body portion 70 and open at the other end into theannular longitudinal melt channel 14 a (best seen in FIG. 2C). In theembodiment shown in FIGS. 2A-2C, the number of longitudinal meltchannels 86 equals four. Only three longitudinal melt channels 86 a-86 cof the four are shown in FIG. 2B, the fourth being located in thecutaway portion of the nozzle 12. The distal body portion 16 of thenozzle 12 has a contoured flow-redirecting surface 80 b (which partlydefines the release melt channel 14 b) and a circular cylindrical outercircumferential surface 84.

The molten filler material 11 inside the longitudinal melt channels 86can be heated during passage through the nozzle 12. The longitudinalmelt channels 86 are configured to guide molten filler material 11 fromthe internal volume 71 of the proximal body portion 70 to flow throughthe nozzle 12 parallel to a longitudinal axis 25 of the nozzle 12. Themolten filler material 11 then continues to flow through annularlongitudinal melt channel 14 a until the molten filler material 11 isredirected by flow-redirecting surface 80 b.

As best seen in FIG. 2C, the flow-redirecting surface 80 b is configuredto divert longitudinally flowing molten filler material 11 exiting theannular longitudinal melt channel 14 a to flow through the release meltchannel 14 b toward the circular circumferential orifice 18. A generallyconical or continuously curved portion of the flow-redirecting surface80 b of the distal body portion 16 and an opposing circular terminaledge 77 of an outer circumferential wall 76 of the intermediate bodyportion 72 define the circular circumferential orifice 18. Theflow-redirecting surface 80 b extends further from the longitudinal axis25 of the nozzle 12 than does the outer circumferential wall 76, i.e.,flow-redirecting surface 80 b has an outermost radius greater than theouter radius of the outer circumferential wall 76. More specifically,the flow-redirecting surface 80 b of the distal body portion 16 of thenozzle 12 is a circumferential surface of revolution having a diameterthat increases continuously to a maximum diameter of the distal bodyportion 16 (i.e., the outer diameter D of the circular cylindrical outercircumferential surface 84) that is greater than an outer diameter ofthe outer circumferential wall 76. The distal body portion 16 preferablyhas a sharp back edge 17 accompanied by a concave end surface 19 to skimthe molten filler material 11 and prevent the molten filler material 11from being pulled radially inward by adhesive forces as the nozzle 12displaces upward during the filling/retraction process.

As best seen in FIGS. 2A and 2B, the intermediate body portion 72 of thenozzle 12 includes a circular cylindrical outer circumferential wall 76having the circular terminal edge 77, which partly defines the circularcircumferential orifice 18. The other side of the circularcircumferential orifice 18 is defined by the flow-redirecting surface 80b of distal body portion 16. In the area of the nozzle 12 depicted inFIG. 2C, the intermediate body portion 72 of the nozzle 12 furtherincludes a circular cylindrical inner circumferential wall 74 that ispreferably concentrically disposed inside the outer circumferential wall76. A surface 80 a of the inner circumferential wall 74 and a surface 78of the outer circumferential wall 76 are respective mutually concentriccircular cylindrical surfaces that define the annular longitudinal meltchannel 14 a that receives molten filler material 11 from thelongitudinal melt channels 86.

In accordance with the embodiment depicted in FIGS. 2A-2C, the innercircumferential wall 74 comprises at least three arc-shaped inner wallsections 74 a-74 c shown in FIG. 2B. In addition, the nozzle 12 furthercomprises radial spacers 88 a-88 d that maintain separation betweeninner circumferential wall 74 and outer circumferential wall 76. Thelongitudinal melt channels 86 (including longitudinal melt channels 86a-86 c) are defined by respective portions of an inner surface of theouter circumferential wall 76, by respective portions of an outersurface of the inner circumferential wall 74, and by respective surfacesof respective pairs of radial spacers 88 a-88 d.

FIG. 3 is a hybrid diagram showing physical and operationalrelationships of some components of an apparatus 1 a for coating asurface of a countersunk hole 20 in a composite layer 30 withelectrically conductive filler material 11 using a linearly retractingand non-rotary nozzle 12 of the type depicted in FIGS. 2A-2C. Inaddition to the equipment which appears in FIG. 1A and which has alreadybeen described, the apparatus depicted in FIG. 3 comprises a reservoir54 designed to hold molten filler material 11. Some of the molten fillermaterial 11 in reservoir 54 may include recycled excess molten fillermaterial 11 received from the recycling pump 56 via pipe 28. A reservoirheating element 36 a, controlled by a heater controller 38, preferablymaintains the temperature of the molten filler material 11 inside thereservoir 54 at less than 200° F. (93.3° C.).

The reservoir 54 is in fluid communication with an internal reservoir 51of a pump assembly 48 via a pipe 64. The pump assembly 48 furtherincludes a motor 44 having an output shaft 62 that is mechanicallycoupled to a screw 52 rotatably mounted inside the internal reservoir51. When the motor 44 is activated by a motor controller 42, the motor44 drives rotation of screw 52, which causes molten filler material 11to be pumped from reservoir 54 to the nozzle 12 via a channel system 68in a retraction guide 66 (see FIG. 9). The nozzle 12 is telescopicallycoupled to slide along the length of the retraction guide 66 duringnozzle retraction. Any suitable actuator 65 and retraction mechanism 67(see FIG. 9) may be provided for retracting the nozzle 12, such as aseparate motor operatively coupled to a pinion, which pinion in turn hasteeth that interengage the teeth of a rack that is connected to thenozzle. Alternatively, a pneumatic or hydraulic cylinder actuated by anelectrically controllable valve or a motor-driven worm gear or variousmotor-driven gear trains could be used to retract the nozzle 12 duringthe gap filling process.

The apparatus 1 a depicted in FIG. 3 further comprises a heating element36 b disposed inside the nozzle 12. The heating element 36 b is alsocontrolled by the heater controller 38. The heater controller 38 ispreferably configured to control the heating elements 36 a and 36 bbased on temperature measurement data received from a temperature sensor(not shown in FIG. 3, but see temperature sensor 40 shown in FIG. 9)placed inside the reservoir 54. Additional temperature sensors may beplaced at strategic locations, e.g., inside the nozzle 12. For example,pyrometers can be employed as a temperature sensor 40.

In accordance with alternative embodiments, a rotary nozzle may be usedto apply a coating of molten filler material 11 on the surface of a hole20 in a composite layer 30. FIG. 4 is a diagram representing one view ofa rotary nozzle 100 a with four circumferentially distributed andlongitudinally extending linear side openings 102 in accordance with oneembodiment. Only linear side openings 102 a and 102 b are visible inFIG. 4. FIG. 4A is a diagram showing a portion of the rotary nozzle 100a depicted in FIG. 4 on a magnified scale, which portion is indicated bythe circle 4A in FIG. 4. FIG. 5 is a diagram representing another viewof rotary nozzle 100 a. FIG. 5A is a diagram showing one portion ofrotary nozzle 100 a on a magnified scale, which portion is indicated bythe circle 5A in FIG. 5. FIG. 5B is a diagram showing another portion ofrotary nozzle 100 a on a magnified scale, which portion is indicated bythe circle 5B in FIG. 5.

The rotary nozzle 100 a depicted in FIGS. 4 and 5 includes a proximalbody portion 70 having a cup shape and an internal volume 71, a circularcylindrical intermediate body portion 72 having an internal channel 73and the aforementioned plurality of linear side openings 102 (includinglinear side openings 102 a and 102 b and two other side openings notshown), and a rounded convex distal body portion 106. The linear sideopenings 102 extend the length of the intermediate body portion 72 andallow molten filler material 11 to exit the internal channel 73. Thelinear side openings 102 also extend into the proximal body portion 70.As best seen in FIGS. 5A and 5B, the nozzle 100 a further includesrespective pairs of beveled projections 104 a and 104 b disposed atopposite edges of each side opening 102. The beveled projections 104 aand 104 b project outward. As best seen in FIG. 5A, each beveledprojection 104 a and 104 b has a cross-sectional shape that resembles aquadrant of a circle. The rounded surface of each beveled projection 104a and 104 b is the surface that deflects molten filler material 11 inits path radially outward as the rotary nozzle 100 a rotates.

During rotation, the rotary nozzle 100 a receives pressurized moltenfiller material 11 and injects molten filler material 11 into the gap 15separating hole 20 and nozzle 100 a until the gap 15 is filled withmolten filler material 11. Concurrently, the leading beveled projections104 a or 104 b (depending on the direction of rotation) push theinjected molten filler material 11 in a direction that has a radiallyoutward component, thereby generating forces that cause the moltenfiller material 11 to flow into and fill any concavities (e.g., crevicesor voids) in the surface of hole 20, in addition to adhering to thesurface of hole 20 with an average thickness δ. The radius at the tipsof the beveled projections 104 establishes the inner diameter D of theresulting coated hole 20 a.

FIGS. 6A and 6B are diagrams representing respective views of a rotarynozzle 100 b having four circumferentially distributed helical sideopenings 108 a-d in accordance with another embodiment. The rotarynozzle 100 b includes a proximal body portion 70 having a cup shape andan internal volume 71, a circular cylindrical intermediate body portion72 having an internal channel 73 and a plurality of helical sideopenings 108 a-d, and a rounded convex distal body portion 106. Thehelical side openings 108 a-d extend along the length of theintermediate body portion 72 and allow molten filler material 11 to exitthe internal channel 73. The helical side openings 108 a-d also extendinto the proximal body portion 70. During rotation, the rotary nozzle100 b injects molten filler material 11 until the gap 15 separating hole20 and rotary nozzle 100 b is filled. The outer diameter of the circularcylindrical intermediate body portion 72 is the same as and establishesthe inner diameter D of the resulting coated hole 20 a.

FIG. 7 is a hybrid diagram showing physical and operationalrelationships of some components of an apparatus 1 b for coating acountersunk hole 20 in a composite layer 30 with electrically conductivemolten filler material 11 using rotary nozzle 100 a (see FIGS. 4 and 5).In the alternative, rotary nozzle 100 b (see FIG. 6) could besubstituted for rotary nozzle 100 a.

The apparatus 1 b depicted in FIG. 7 comprises a reservoir 54, arecycling pump 56, and connecting pipes 26, 28 and 64 as previouslydescribed. Molten filler material 11 is provided from reservoir 54 to aninternal reservoir 51. A screw 52 inside the internal reservoir 51 isdriven to rotate by a motor 44 that is operatively coupled to the screw52 by means of a first gear train comprising a first gear 94 mounted tothe output shaft 45 of motor 44 and a second gear 92 mechanicallycoupled to the shaft (not shown) of the screw 52. During rotation ofscrew 52, the screw 52 forces molten filler material 11 into the rotarynozzle 100 a for injection into hole 20. The rotary nozzle 100 a isdriven to rotate by a motor 60 that is operatively coupled to the rotarynozzle 100 a by means of a second gear train comprising a third gear 98mounted to the output shaft 61 of motor 60 and a fourth gear 96mechanically coupled to the rotary nozzle 100 a.

FIG. 8 is a hybrid diagram showing physical and operationalrelationships of some components of an apparatus 1 b for coating a hole20 in a composite layer 30 with electrically conductive molten fillermaterial 11 using a rotary nozzle 100 c. In this embodiment, the hole 20has neither a countersink nor a counterbore such that the chamfer 21 isomitted. Therefore the rotary nozzle 100 c is suitably configured toinject molten filler material 11 into hole 20. The other componentsdepicted in FIG. 8 are the same as those depicted in FIG. 7.

FIG. 9 is a block diagram identifying some additional components of theapparatus 1 a partly depicted in FIG. 3. The apparatus 1 a includes acontrol computer 50 that executes instructions stored in anon-transitory tangible computer-readable storage medium that may beincorporated in or external to the control computer 50. The controlcomputer 50 is operatively coupled to the motor controller 42 and theheater controller 38 by two-way communication links.

The motor controller 42 includes a separate computer or processor thatis programmed to receive pressure measurement data from a pressuresensor 46 and control the motor 44 as a function of pressure dataobtained by the pressure sensor 46. The pressure sensor 46 may belocated inside any component that holds molten filler material 11 sincethe latter is an incompressible fluid having the same pressureeverywhere in the flow circuit. The apparatus 1 a is scalable and theflow rate at the circular circumferential orifice 18 (see FIG. 1)depends on the required release rate, orifice cross-sectional area,and/or the static pressure of the molten filler material 11. Theapparatus 1 a must maintain a relatively constant pressure duringrelease. For instance, if the nozzle 12 is moving up and suddenly thereis relatively large gouge in the hole surface, the sudden additionalvolume of the gap 15 separating nozzle 12 and hole 20 takes a relativelylarge amount of molten filler material 11, thereby causing the pressureto drop for a fraction of a second. The feedback loop among the controlcomputer 50, the motor controller 42, and the heater controller 38 isconfigured to compensate to maintain the pressure by increasing the flowof molten filler material 11.

Still referring to FIG. 9, the heater controller 38 also comprises aseparate computer or processor that is programmed to receive temperaturemeasurement data from a temperature sensor 40 and control the heatingelements 36 a and 36 b as a function of the temperature measurementdata. More than one temperature sensor 40 may be placed at strategiclocations, including inside the nozzle 12.

In accordance with the embodiment depicted in FIG. 9, the controlcomputer 50 can be configured to coordinate the operations of the heatercontroller 38 and motor controller 42. In accordance with an alternativeembodiment, the measurement data acquired by the temperature sensor 40and pressure sensor 46 may be received by the control computer 50, inwhich case the heater controller 38 and motor controller 42 can becontrolled by the control computer 50. For example, the control computer50 reads the pressure and temperature measurement data and outputsheater power control signals that control the power supplied to theheating elements 36 a and 36 b in a closed-loop control system. Theheater power control signals are sent by the control computer 50 to asignal conditioner (not shown), which in turn outputs conditioned heaterpower control signals to the heater controller 38. The heater controller38 is configured to convert conditioned heater power control signals toan output voltage which is used to power the heating elements 36 a and36 b.

In addition, the control computer 50 may be configured with programmingfor controlling the retraction motion of the retractable nozzle 12. Aspreviously mentioned, the actuator 65 may comprise a motor, while theretraction mechanism 67 may comprise any one of a plurality of differenttypes of motor-driven gear trains. Alternatively, the actuator 65 maycomprise an electrically controllable valve, while the retractionmechanism 67 may comprise a pneumatic or hydraulic cylinder. In eachcase, the actuator 65 and retraction mechanism 67 are responsive tocontrol signals received from the control computer 50.

In accordance with one proposed implementation, the control computer 50is configured with programming for controlling a rate of rotation of thescrew 52 of the pump assembly 48 and a rate of displacement of theretraction mechanism 67 during a filling operation. In accordance withan alternative proposed implementation, the control computer 50 isconfigured with programming for controlling a rate of rotation of thescrew 52 and a rate of rotation of the rotary nozzle 100 a during afilling operation.

There are generally two options for the insertion/retraction of bothnon-rotary and rotary nozzles. The apparatuses 1 a and 1 b depicted inFIG. 3, 7, or 8 can be attached to the end effector of a robot arm (notshown in the drawings), in which case the robot arm can move theapparatus 1 a or 1 b toward and away from a workpiece. A telescopicmechanism can be used to insert or retract the nozzle 12. In accordancewith one proposed methodology that employs a rotary nozzle 100 a, 100 b,or 100 c, first the nozzle 12 is centered in the hole 20. Then therotary nozzle 100 a, 100 b, or 100 c is rotated to inject molten fillermaterial 11 into the hole 20. Once the nozzle rotation (or multiplerotations) is complete, the nozzle 12 is retracted.

In many aircraft applications, the composite material comprises carbonfiber-reinforced plastic (CFRP). The structural integrity of CFRPmaterial may be compromised at a temperature over 254° F. (123.3° C.).Accordingly, it is preferred that the electrically conductive fillermaterial comprise low-melting alloy that melts at a temperature wellbelow 254° F. (123.3° C.), for example, below 200° F. (93.3° C.), isused as the molten filler material 11. FIG. 10 is Table 1 listing samplecompositions of filler materials which meet the foregoing criterion andare suitable for use as the molten filler material 11 in the methodsdisclosed in some detail hereinabove. These gap filler materials includeor are gallium-based alloys of liquid metal combined with a pure solidmetal or with a solid metal alloy.

As can be seen in Table 1, gallium alloys are formed by combininggallium with one or both of tin and indium. These metal alloys areinitially in a liquid state at about room temperature below 30° C. Theliquid metal alloy containing gallium is then mixed with a solid metalor solid metal alloy in either a powder or film state. The particle sizeor film thickness may be between 50 nanometers and 100 microns. As canbe seen in Table 1, the solid metal mixed with gallium alloy is selectedfrom the group consisting of pure nickel, pure copper, or pure silver.Bronze can be selectively used to mix with the liquid gallium metalalloy. Table 1 shows the material elemental weight ratios of thechemical components to be mixed to create each sample filler material.

With the mixing of gallium alloy with solid metal or solid metal alloy,the resulting slurry or paste-like consistency enables properapplication of the molten filler material 11 to conform to the roughenedsurface of the hole 20 in the composite layer 30. After the nozzle 12 isremoved from the hole, the molten filler material 11 cures to a solidstate coating 11 a.

An additional mechanical reinforcing phase can be added to the slurry ofthe mixture of the liquid gallium metal alloy with a solid metal orsolid metal alloy. This mechanical phase will provide enhanced shearresistance to the cured solidified alloy. This mechanical phase materialcan selectively include one of the following: pure cobalt, puretungsten, pure molybdenum, pure titanium, a titanium alloy (such as AMS4911), or a stainless steel (such as 302 or 316).

Since the distal body portion 16 of the nozzle 12 can be center-lessground to a specific diameter, the effective hole size will becontrolled by the diameter of the distal body portion 16 rather than thedrilling process. This change can reduce the variability of diameters ofholes 20 and allow for less variation in the interference levels betweenthe fastener 7 and the hole 20 (reducing process variation and allowingfor increased cutter life). By compressing the conductive molten fillermaterial 11 into the voids in the surface(s) of the hole 20, theelectrical conductivity, the fatigue life, and/or fluid-tight propertiescan be improved as compared to conventional hole formation andpreparation.

In addition, the coating 11 a of solidified filler material cancompensate for anomalies in the surface(s) of the hole 20 that mayresult during the hole drilling process due to the thickness of thecoating 11 a. For example, the coating 11 a of solidified fillermaterial can compensate for a 1° offset of an axis of the hole 20. Thegap filling process disclosed above can be employed with many differenttypes of interference fit fastener assemblies. For the sale ofillustration, once such interference fit fastener assembly will now bedescribed.

As seen in the partially sectioned view shown in FIG. 11, the result ofthe hole drilling and hole coating processes disclosed above is astructural assembly 5 that can be incorporated in an aircraft. Thestructural assembly 5 includes a composite layer 30 having a hole 20with a relatively rough surface that has crevices. The structuralassembly 5 also includes a coating 11 a adhered to the hole 20 whilefilling the crevices. The coating 11 a defines a circular cylindricalcoated hole 20 a having a relatively smooth surface. The composite layer30 has fibers made of electrically conductive material and the coating11 a includes or is an electrically conductive low-melting alloy, suchas those described with respect to FIG. 10. As seen in FIG. 11, thisstructural assembly 5 may further include a layer 32 of structuralmaterial disposed adjacent to and in contact with the composite layer30.

The structural assembly 5 also includes a sleeveless interference fitfastener assembly 2 having a fastener 7 and a swaged collar 34. Thefastener 7 includes a shank 6, a threaded portion 8, and a transitionportion 10. In alternative embodiments, the fastener 7 may have externalannular rings instead of external threads. Although FIG. 11 depicts afastener 7 having a countersunk (i.e., flush) head 4, fastener 7 may inthe alternative have a protruding head. An interference fit is achievedby providing a coated hole 20 a having an inner diameter D that is lessthan the outer diameter of the shank 6 (e.g., a difference of a fewthousandths of an inch).

The fastener 7 shown in FIG. 11 is inserted into the coated hole 20 afrom one side of the joint structure and the unswaged collar (not shownin FIG. 11) is placed over the fastener 7 from the other side of thejoint structure. Access to both sides of the joint structure isrequired. During the installation cycle of the fastener 7, the unswagedcollar (in the form of a loose-fitting metal ring) is deformed aroundthe fastener 7, which has locking grooves on the threaded portion 8. Thefastener 7 and swaged collar 34 combine to form the fastener assembly 2.

The bolts and pins disclosed herein are preferably made of a metal alloysuch as titanium alloy, aluminum alloy, Inconel or corrosion-resistantsteel. The collars disclosed herein are preferably made of titaniumalloy, aluminum alloy or corrosion-resistant steel.

FIG. 12 is a flowchart identifying steps of a method 120 for injectingmolten filler material 11 into a hole 20 in accordance with oneembodiment. The method 120 comprises: (a) drilling a hole 20 in acomposite layer 30 (step 122); (b) heating filler material comprising anelectrically conductive low-melting alloy to a molten state to producemolten filler material 11 (step 124); (c) inserting a nozzle 12 havingan internal channel system 13 into the hole 20 with a gap 15 separatingthe nozzle 12 and the hole 20 (step 126); (d) forcing the molten fillermaterial 11 into, through, and out of the internal channel system 13 ofthe nozzle 12 and into the gap 15 (step 128); and (e) retracting thenozzle 12 from the hole 20 (step 130). The molten filler material 11cools to form a coating 11 a on the surface(s) of the hole 20. Afastener 7 is inserted into the coated hole 20 a, as described above, tocouple layers 30, 32 of material together using the interference fitfastener assembly 2.

While apparatus and methods for injecting molten filler material into ahole in a composite layer have been described with reference to variousembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the claims setforth hereinafter. In addition, many modifications may be made to adaptthe teachings herein to a particular situation without departing fromthe scope of the claims.

In the event that the annexed claims are amended during prosecution toinclude the term “computer system”, that term should be construedbroadly to encompass a system having at least one computer or processor,and which may have multiple computers or processors that communicatethrough a network or bus. As used in the preceding sentence, the terms“computer” and “processor” both refer to devices comprising a processingunit (e.g., a central processing unit, an integrated circuit or anarithmetic logic unit). For example, in an embodiment where the heatercontroller 38, motor controller 42 and control computer 50 each compriseat least one processor, all of those processors may be deemed to becomponents of a “computer system” if, for example, the control computercommunicates with both the heater controller 38 and the motor controller42.

The method claims appended hereto should not be construed to requirethat the steps recited therein be performed in alphabetical order (anyalphabetical ordering in the claims is used solely for the purpose ofreferencing previously recited steps) or in the order in which they arerecited unless the claim language explicitly specifies or statesconditions indicating a particular order in which some or all of thosesteps are performed. Nor should the process claims be construed toexclude any portions of two or more steps being performed concurrentlyor alternatingly unless the claim language explicitly states a conditionthat precludes such an interpretation.

The invention claimed is:
 1. A method for injecting molten fillermaterial into a hole, the method comprising: (a) drilling the hole in acomposite layer; (b) heating filler material comprising an electricallyconductive low-melting alloy to a molten state to produce the moltenfiller material; (c) inserting a nozzle having an internal channelsystem into the hole with a gap separating the nozzle and the hole; (d)forcing the molten filler material into, through, and out of theinternal channel system of the nozzle and into the gap; and (e)retracting the nozzle from the hole.
 2. The method as recited in claim1, further comprising rotating the nozzle as the molten filler materialexits the nozzle.
 3. The method as recited in claim 2, wherein themolten filler material exits the nozzle through a plurality ofcircumferentially distributed side openings.
 4. The method as recited inclaim 1, wherein the molten filler material exits the nozzle duringretraction of the nozzle.
 5. The method as recited in claim 4, whereinthe molten filler material exits the nozzle through a circularcircumferential orifice and is redirected and pushed in a directionhaving a radially outward component by a contoured flow-redirectingsurface of the nozzle during retraction of the nozzle.
 6. The method asrecited in claim 1, further comprising guiding excess molten fillermaterial to flow from the gap to a reservoir external to the hole. 7.The method as recited in claim 1, wherein step (a) comprises drilling ahole that has a chamfer in an uppermost portion of the hole, the methodfurther comprising guiding a flow of the molten filler material to coata surface of the chamfer.
 8. The method as recited in claim 1, furthercomprising heating the molten filler material as the molten fillermaterial flows through the internal channel system of the nozzle.
 9. Themethod as recited in claim 1, wherein the nozzle is retracted until thenozzle is completely removed from the hole, the method furthercomprising inserting a fastener into the hole with an interference fit.10. The method as recited in claim 9, further comprising heating thefastener before insertion.
 11. An apparatus for injecting molten fillermaterial into a hole, the apparatus comprising: a reservoir for storingthe molten filler material that is electrically conductive; a pumpassembly in fluid communication with the reservoir; and a nozzle influid communication with the pump assembly for receiving the moltenfiller material pumped from the reservoir and ejecting the molten fillermaterial, wherein the nozzle comprises: a proximal body portion havingan internal volume in fluid communication with the pump assembly; anintermediate body portion comprising a plurality of longitudinal meltchannels configured to guide the molten filler material entering fromthe internal volume of the proximal body portion to flow parallel to alongitudinal axis of the nozzle and away from the proximal body portion;and a distal body portion comprising a flow-redirecting surfaceconfigured to divert a longitudinal flow of the molten filler materialto flow radially outward from the nozzle, wherein a portion of theflow-redirecting surface of the distal body portion and a portion of theintermediate body portion define a circular circumferential orifice. 12.The apparatus as recited in claim 11, wherein the intermediate bodyportion of the nozzle comprises an outer circumferential wall having acircular terminal portion, and a portion of the intermediate bodyportion that partly defines the circular circumferential orificecomprises the circular terminal portion of the outer circumferentialwall.
 13. The apparatus as recited in claim 12, wherein the intermediatebody portion of the nozzle further comprises: an inner circumferentialwall; and a plurality of radial spacers that maintain separation betweenthe inner circumferential wall and the outer circumferential wall,wherein the longitudinal melt channels are defined by respectiveportions of an inner surface of the outer circumferential wall, byrespective portions of an outer surface of the inner circumferentialwall, and by respective surfaces of respective pairs of radial spacers.14. The apparatus as recited in claim 12, wherein the flow-redirectingsurface of the distal body portion of the nozzle is a circumferentialsurface of revolution having a diameter that increases continuously to amaximum diameter of the distal body portion that is greater than anouter diameter of the outer circumferential wall.
 15. The apparatus asrecited in claim 11, further comprising: a recycling pump in fluidcommunication with the reservoir; a pipe in fluid communication with therecycling pump; and an end cap in fluid communication with the pipe,wherein the end cap is configured to sit atop the hole in a compositematerial and cover a volume of space that is in fluid communication withthe pipe and have an opening through which a portion of the nozzle ispassed.
 16. The apparatus as recited in claim 11, further comprising: aretraction mechanism for retracting the nozzle; and a control computerconfigured with programming for controlling a rate of rotation of thepump assembly and a rate of displacement of the retraction mechanismduring a filling operation.
 17. The apparatus as recited in claim 11,further comprising a heating element disposed inside the nozzle.
 18. Anapparatus for injecting molten filler material into a hole, theapparatus comprising: a reservoir for storing the molten filler materialthat is electrically conductive; a pump assembly in fluid communicationwith the reservoir; a rotary nozzle in fluid communication with the pumpassembly for receiving the molten filler material pumped from thereservoir and ejecting the molten filler material; and a motor fordriving rotation of the rotary nozzle, wherein the rotary nozzlecomprises a circular cylindrical intermediate body portion having aninternal channel system and a plurality of side openings that arecircumferentially distributed and extend a length of the circularcylindrical intermediate body portion and allow the molten fillermaterial to flow radially outward from the rotary nozzle, and whereinthe plurality of side openings are linear or the plurality of sideopenings are helical.
 19. The apparatus as recited in claim 18, furthercomprising respective pairs of beveled projections disposed at oppositeedges of each side opening.
 20. The apparatus as recited in claim 18,further comprising a control computer configured with programming forcontrolling a rate of rotation of the pump assembly and a rate ofrotation of the rotary nozzle during a filling operation.
 21. Astructural assembly for an aircraft, the structural assembly comprising:a composite layer having a hole with a relatively rough surface that hasconcavities; and a coating adhered to the relatively rough surface ofthe hole and filling the concavities, the coating defining a smoothcircular cylindrical surface of a coated hole, which smooth circularcylindrical surface circumscribes an empty space, wherein the compositelayer comprises fibers made of electrically conductive material and thecoating comprises an electrically conductive low-melting alloy.